1. DIGESTION OF ORAL CAVITY AND STOMACH

2. ORAL CAVITY PHYSIOLOGICAL EVENTS 1. Ingestion 2. Mechanical digestion
3. Chemical digestion
4. Propulsion voluntary stage of swallowing

3. ORAL CAVITY
1. Ingestion of food is simply voluntarily taking food into the digestive tract through the oral cavity.

4. ORAL CAVITY 2. MECHANICAL PROCESSES Mastication
As food enters the oral cavity the cheeks and the closed lips hold food between the teeth, the tongue mixes the food with saliva to soften it, and the teeth cut and grind it into a bolus. Suitable for swallowing
Mastication is both voluntary and partly reflexive.

5. ORAL CAVITY 3. Chemical processes
Chemical digestion of starch is begun by salivary amylase present in saliva.
Saliva (1-1,5 liters per day) is a slightly acid solution of salts and organic substances secreted mainly by 3 pairs of salivary glands (parotid, buccal, submandibular glands).
Basic saliva components:
• Water 99.5%
• Ions: Na+, K+, Ca2+, Cl–, HCO3–
• Proline-rich proteins for protection of teeth enamel:
- Enzymes: ptyalin (from salivary glands),
**lingual lipase (secreted from glands on the tongue).
- Immunoglobolins: IgA
- Mucin: glycoproteins for lubrication of food and protection of oral mucosa
- Lysozyme, lactoferrin, thiocyanate ions
pH of saliva is about 7
Salivary flow ranges between 0.5 ml/min during basal flow and 5ml/min during maximum flow

6. ORAL CAVITY Other important (non-digestive) functions of saliva:
Cleansing – Mouth and teeth kept free of debris, ect.
Protection – Leucocytes, the enzyme lysozyme and antibodies act against some bacteria.
Moistening and Lubricating – soft parts of mouth kept pliable for speech. Cells of oral mucosa protected from drying.
Excretory – many organic substance (e.g. urea, sugar) and inorganic substance (e.g. mercury, lead) can be excreted in saliva.

7. ORAL CAVITY 4. PROPULSION
The voluntary phase of deglutition is initiated by the tongue. The tip of the tongue is place on the hard palate, and then contracts which forces the bolus into the oropharynx.

8. Autonomic nerves Cerebral cortex Other inputs Salivary center
in medulla
Conditioned
reflex
Autonomic nerves
Autonomic nerves
Pressure receptors
and chemoreceptors
in mouth
Simple reflex
Salivary glands
Salivary secretions

9. PHARYNX 1. Chemical digestion PHYSIOLOGICAL EVENTS
Carbohydrate digestion continues. This is due to fact that the pH of the pharynx is slightly acid to neutral as is the oral cavity.
No other marcomolecule begins chemical digestion.

10. PHARYNX
2. PROPULSION
The pharyngeal phase of deglutition is initiated by food in the oropharynx. The presence of food causes the tongue to blocks off the oral cavity, the soft palate to rise and close off the nasopharynx.
In addition, the larynx to rise so that the epiglottis covers the opening into the respiratory system, and the upper esophageal sphincter to relax and open.

11. Esophagus
Bolus (moistened ball of chewed up food) is forced into the pharynx.
The epiglottis prevents food from entering the trachea during swallowing, and passes bolus into the esophagus
The esophagus is a muscular tube that connect pharynx to the stomach.
The series of rhythmic contractions & relaxations is called peristalsis. Peristalsis pushes the bolus through the esophagus into the stomach.

12. The Swallowing Process
Is also called deglutition
Can be initiated voluntarily, Proceeds automatically
Is divided in 3 phases:
buccal phase – Compression of bolus against hard palate, Retraction of tongue forces bolus into oropharynx:
pharyngeal phase – Bolus contacts: arches and posterior pharyngeal wall
esophageal phase - Contraction of pharyngeal muscles forces bolus through entrance to esophagus Primary Peristaltic Waves

13. STOMACH 3 muscle layers: oblique, circular, longitudinal Regions:
Cardiac sphincter
Fundus
Antrum (pylorus)
Pyloric sphincter
Vascular
Inner surface thrown into folds – Rugae
Contains enzymes that work best at pH 1-2

14. Functions of stomach Mix food Reservoir Start digestion of
- Protein
- Nucleic acids
- Fats
Activates some enzymes
Destroy some bacteria
Makes intrinsic factor – B12 absorption
Absorbs
- Alcohol
- Water
- Lipophilic acid
- B12

15. Exocrine gastric glands
Golbet cells mucus;
Pariental cells hydrochloric acid (HCl);
Chief (or zymogenic) cells pepsinogen,
an inactive form of the protein-digestive enzime pepsin;
Enterochromaffin-like (ECL) cells histamine and serotonin
as paracrine regulalators of the GI tract;
G cells gastrin into the blood;
D cells hormone somatostatin.

16. STOMACH Mechanical digestion
The walls of the stomach have several muscle layers. These muscles work together to churn the food, breaking up food particles and mixing them with gastric fluid. This results in a mixture called chyme. Chyme moves from the stomach to the small intestine.
Gastric glands release gastric juice, a mixture of mucus, digestive enzymes, and hydrochloric acid.

17. STOMACH Gastric fluid carries out chemical digestion in the stomach
Hydrochloric acid ensures a low pH in the stomach, dissolves minerals and kills bacteria
An enzyme called pepsin begins the break down of proteins into peptide chains (chains of amino acids). Pepsin functions in a pH of about 2.
Mucus coats the stomach and protects it from HCl & digestive enzymes
When the mucus coating breaks down allowing digestive enzymes to eat through part of the stomach lining, the result is called an ulcer.

18. STOMACH
PROPULSION
After a meal, peristalsis begins near the cardiac region and moves toward the pyloric sphincter. The intensity of the movements are due to the increase in the number of muscle layers of the stomach.

19. STOMACH The pyloric region of the stomach holds about 30 ml of
chyme. It allows only liquids
and small particles of chyme,
about 3 ml, to pass through
the valve for each peristaltic
wave. The contractions of
the pylorus decrease the
opening of the valve. This
results in the remaining
chyme being remixed again
and again.

20. STOMACH The rate of peristaltic waves is constant 3/min., however,
the intensity can be modified.
This contractile rhythm is set
by the spontaneous activity of
pacemaker cells located in the
longitudinal smooth muscle
layer. This cells establishes
the basic electrical rhythm of
the stomach.

21. STOMACH The stomach usually empties completely within 4 hours after a
meal. The rate of
gastric emplying
depends on the
contents of the
duodenum as on what
is happening in the
stomach.

22. Mechanism for secretion of hydrochloric acid
Extracellular
fluid
Pariental cell
Lumen of canaliculus

23. Stomach neurological control

24. Stomach neurological control
1. CEPHALIC PHASE
Slight, thought, taste, or smell of food causes stimulation of the vagus. The vagus stimulates the production of gastric juice.

25. Stomach neurological control
2. GASTRIC PHASE
Stomach distention will act locally or evoke the vagovagal reflex.
VAGOVAGAL
REFLEX
Vagovagal
reflex

26. Stomach neurological control
3. INTESTINAL PHASE

28. Stomach hormonal control
MECHANICAL DIGESTION
1. Gastrin--stimulate gastric emptying
2. Serotonin--contraction ofsmooth muscle
3. Somatostatin--inhibits motility and emptying
4. Secretin--inhibits gastric motility
5. Gastric Inhibitory Peptide--inhibits gastric motility

29. Stomach hormonal control
CHEMICAL DIGESTION
1. Gastrin--stimulates gastric secretions
2. Histamine--stimulates HCl formation
3. Somatostatin—inhibits gastric secretions
4. Secretin--inhibits gastric secretions
5. Gastric inhibiory peptide--inhibits gastric secretions
6. Vasoactive intestinal peptide-inhibits HCl production

30. Stomach hormonal control
PROPULSION
1. Gastrin--stimulates emptying
2. Somatostatin--inhibits gastric motility and emptying
3. Secretin--inhibits gastric motility and emptying
4. Gastric Inhibitory Peptide—inhibits gastric motility and emptying

31. Mouth
break up food
digest starch
kill germs
moisten food
Stomach
break up food
digest protein
kill germs
store food